Radio receiver



lo'Y

c. s. Roo'r RADIO RECEIVER Filed July 19 1943 I 15-;- AUDIO AUDIO FREQUENCY FREQUENCY WAVE AMPLIFIERS SOURCE AND REPRODUCER 5 H I J i i ,o- 8 LO- Q U 3 U 2 1 g O s 505- 0.5 E 5 0 I00 400 3,000 4,000 |00o 0 I00 400 3,000 4,000 10,000 FREQUENCY CYCLES PER.sEc FREQUENCY CYCLES PER. sEc.

Ihventor 7 Charles 5.,Root,

His ttorfney.

Patented Jan. 1945 RADIO RECEIVER Charles S. Root, Fairfield, Conn, assignor to General Electric Company, a corporation of New York Application July 19, 1943, Serial No. 495,282 I 11 Claims.

My invention relates to radio receivers, more particularly to tone control circuits for such receivers, and has for its principal object a new and improved simple, reliable, and inexpensive tone control arrangement particularly suitable for receivers of the household type.

Tone controlcircuits are commonly used at the present time for controlling the low, intermediate, and high audio frequency response for radio receivers in order that an individual may select the frequency characteristic most pleasing to him, or correct for the acoustic characteristics of the particular ro'omin which the radio receiver maybe located. Such circuits are also useful'for-removing undesired oscillations, such as noise caused by so-calledstatic or low frethat two or three values of low frequency -re- 1 sponse are ordinarily entirely adequate tomeet quency howl commonly experienced in short wave reception. Ordinarily, tone control is effected by controlling the low and high frequency response relative to the intermediate frequency response.

way to do this isby Theoretically, the ideal means-of two' individual continuous controls so that both the low and high frequency response may be separately adjusted asdesired. 'In practice, however, it has been found that the provision of two tone controls is not only expensive but also so confusing to the average person that he is quite apt to misuse both of them.

One way of controlling both low and high frequency response with a single control is to provide a switch for selecting separate circuit components providing two or more degrees of low frequency response and other circuit components providing two or more degrees of high frequency response, Four switch positions are required to provide two degrees of low frequency response for each sponse. Because of the four fixed positions, such a switch is both expensive and complex, and at best provides only a certain limited number of degrees of response.

vIt is also possible to provide continuous control of both low and high frequency response -with a single controlmember by connecting a potentiometer in 'such a way that movement over one-half of its range controls the low frequency response with the high frequency response fixed, while movement over the other. half of its range controls the high frequency response with the low frequency response fixed. However, such an arrangement has the disadvantage that the one response must be fixed while the other response is being adjusted. In

general, the single value'of fixed response is not an optimum for all values of the variable response. I

Experience has shown that a continuous high frequency control is very desirable in order to 'provide a large selection of values of high frequency response. On the other hand, a continuous control of low frequency response is not always necessary and, infact, it has been found all conditions of operation, particularly when combinedwith a control.

Accordingly, it is a further object of my invention to provide a new and improved tone control circuit comprising a single control member movable to select a desired number of degrees of response to one band of audio frequencies and by the same movement continuously" to control the degree of response to a second band of audio frequencies and over the same range for each selected degree of response to the first band of frequencie It is a further object of my'invention to provide a new and improved tone control circuit including a volume control resistor. and a manually operable member movable continuously to control the-intensity tions impressed upon said resistor and by the same movement to control the intensity of low frequency oscillations appearing across ,saidxresistor.

My invention values of one response and continuous control sponse all in one control member. of two degrees of high frequency re- I the accompanying drawing,

of.the otherresponse over the same range ofvalues for each selected value of the first re- By way of example, I have shown the selection more values as applied to the low frequency response and the continuous control applied to the high frequency response.

My invention itself will be more fully understood and its objects and advantages further appreciated by referring now to the, following detailed specification taken in conjunction with schematic circuit diagram'of a radio receiving apparatus embodying my invention in one form;

Figs. 2 and 3 are schematic circuit diagrams of radio receiving systems embodying certain other forms of my invention; and Figs. 4 and 5 are graphical representations of certain of the characteristics of my invention.

Referring now to the drawing, I have shown at Fig. 1 a radio receiving apparatus comprising continuous high frequencyof high frequency oscil1a-- provides two or more different of two or in which Fig. 1 is a amplitude modulated or frequency modulated signal waves, and may be either of the superheterodyne type or comprise a plurality of stages tact 22 is in engagement with the contact ring 23, the capacitor I6 is .short-circuited to ground so that the bass compensation described above is ineffective. When the potentiometer arm 20 is of radio frequency amplification preceding the.

detector. The detected output from the source H, which is of audio frequency varying in accord with voice or music, is impressed across a volume control load resistor l2 having one terminal grounded at 13 and provided with a variable potentiometer slider l4. Across a selectable portion of the volume control resistor- I2, the potentiometer slider l4 supplies an audio frequency signal wave to a suitable signal reproducing apparatus 15. The apparatus l5 prefer-,

ably comprises one or more stages of audio frequency amplification and a signal reproducing device, such as a loud speaker, having a voice coil a.

Shunted across a portionof the volume control resistor 12, is connected a bass compensation" capacitor It in series circuit relation with a resistor H. The capacitor I6 is substantially ineffective for high and intermediate frequency oscillations applied to the volume control resistor i2 by reason of the fact that at these frequencies its impedance is small. However, as is well known, the impedance of the condenser IS increases with decreasing frequency of oscillation so that for low frequencies the shunt circuit through the capacitor It provides a substantially greater impedance than for higher frequencies. The greater impedance of the capacitor l6 for low frequencies increases the low frequency voltage drop across the lower portion of the resistor 12 relative to the high and intermediate frequency voltage drops across the same portion of the resistor. 'I'l1us,the volume setting of the slider 14 is effectively higher for low frequency oscillations than for high and intermediate frequency oscillations. In this manner the low,'or bass, notes are emphasized.

For the purpose of attenuating only the high frequency oscillations supplied to the volume control resistor l2, an adjustable high frequency by-pass circuit comprising a high cutting" capacitor I8 is connected in series circuit relation on the Opposite side of its mid-position thereby to disengage the contacts 22 and 23, the capacitor I6 is rendered operable.

It will now be observed that I have provided a control potentiometer i9, so arranged that when the potentiometer arm '20 is moved to the left from its mid-position, as shown in the drawwith a potentiometer resistor l9. According to v the modification of the invention shown at Fig. 1, the opposite terminals of the potentiometer resistor l9 are connected together and to the'capacitor l8; whilea brush arm 20, arranged for sliding contact along the resistor i9, is grounded at 2!. With this connection, the sections of the potentiometer resistor IS on opposite sides of the brush arm 20 are connected in parallel circuit relation and in series with the capacitor 18 across the entire volume control resistorl 2. By moving the brush arm 20 in either direction from its midposition', the resistance connected in series with the capacitor, It! may be decreased, thereby to control the effectiveness of the capacitor IS in by- 1 passing the high frequency oscillations selected side of its mid-position. -When the coning, it controls continuously the effectiveness of the high cutting capacitor I8 over a predetermined range with the bass compensation" capacitor IS in operation. When the potentiom-- eter arm is moved to the right of its mid-position as viewed at Fig. 1, it controls continuously the effectiveness of the capacitor l8 over the same range and also disables the bass compensation" capacitor [6. One important feature of this arrangement is that it provides one position of the potentiometer arm 2!], namely, the extreme righthand position, where maximum attenuation of both the high frequency and the low frequency oscillations is attained. This position is important for cutting out simultaneously both high and low frequency noises. It also has the effect of reducing the tendency of the receiver to howl," or produce fluttering .sounds due to acoustic feedback between the loud speaker and oscillator, such as occurs frequently during short wave reception. The maximum attenuation of the high freqpency oscillation is attained by short-circuit- -ing of the potentiometer resistor l9, and maximum attenuation of the low frequency oscillations is obtained by disabling of the capacitor IS. The frequency response characteristics of my invention are best illustrated by a group of curves such as those reproduced at Figs. 4 and 5. These curves show the manner in which the voltage on the'voice coil [5a, as a measure of sound intensity, varies with frequency for an input wave of predetermined magnitude. Fig. 4 shows a family of curves representing frequencygesponse at various positions of the potentiometer arm 20 to the left of its mid-position (Fig. 1). It will be noted from Fig. 4 that for any position of the arm 20 to the left of its mid-position, the low frequency response is high and substantially unlow and substantially the same throughout the entire range of high frequency control, while when the arm 20 is to theleft of center the low frequency response is high and substantially the same through the same range of high frequency control.

It will be evident to those skilled in the art that my invention is not limited to the particular potentiometer connection or short-circuiting switch arrangement shown at Fig. 1. At Figs. 2 and 3, I have illustrated certain modifications of, my combined high and low frequency tone control member. I

The receiving system of Fig. 2, except for the connections of the tone control potentiometer, is

similar in all respects to the system'shown in a tone control potentiometer including a variabl resistor Na and a manually operable sliding contact.20a cooperating therewith. According to the arrangement herein shown, the mid-point of the potentiometer resistor Illa is connected to the condenser l8 and the manually operable slider a is grounded. Thus, with the connections I shown at Fig. 2, maximum attenuation of the high frequency oscillations supplied to the resistor I2 is attained when the potentiometer slider ZlIa-is at its'mid-position. Movement, of the slider 20a to either side of its mid-position increases the resistance in series with the capacitor l8 and decreases th effectiveness of the capacitor I8. It will be noted, however, that as at Fig. 1, the two impedance sections of the potentiometer resistor l9a on opposite sides of the mid-point control the effectiveness of the capacitor I 8 over the same range of tone control.

In place of the sliding contact switch of Fig. 1,

I have shown at Fig. 2 an overcenter switch.

high frequency tone control is possible over a wide and continuous range with the capacitor l6 in operation. When the potentiometer arm 20a is moved past its mid-position and on to the right side of the potentiometer resistor l9a, as viewed at Fig. 2, it actuates the switch arm 22a into engagement with the grounded contact 123a. Thus, when the slider 20a is on the right, side of its mid-position, high frequency tone control over the same predetermined range is possible with. th capacitor l6 disabled.

At Fig. 3, I have shown a still further modification of my invention wherein the tone control potentiometer comprises two separate and similar impedance sections, each having one terminal connected to the capacitor I 8. Specifically, the potentiometer resistor comprises two separate similar resistor sections 25 and 26 having opposite terminalsconnected together and to the capacitor l8. Inall other respects th arrangement of Fig. 3 is similar to that illustrated in Fig. 2 and like .parts have been assigned the same reference-numerals. It will be evident almost by inspection that the arrangement of Fig. 3 differs from that of Fig. 2 only in that the potentiometer arm 20a, in moving to the left of its mid-position as viewed in the drawing, decre es the resistance in series with the capacitor the right of its mid-position, as viewed in the drawing, rather than at the extreme right-hand slider 20a on the left section of the resistor l9a,

position as at Fig. 1.

The frequency response curves of Figs. 4 and 5 are, of course, also characteristic of the forms of my invention shown at Figs. 2 and 3. Although I have shown the high cutting capacitor l8 connected in parallel circuit relation to the volume control potentiometer [2, it will be apparent tothose skilled in the art that this capacitor may with equal facility be connected between other suitable points in the audio frequency circult and ground.

While I have illustrated only certain preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled. in the artv and I therefore wish to have it understood that I intend by the appended claims to cover all such modifications asfall within th true spirit-and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a load circuit, means for supplying to said load circuit electric oscillations varying in frequency within a band of audible frequencies in accordance with desired signals,.

means for attenuating high frequency oscillations supplied to said'load circuit, separate means for increasing the intensity of low frequency oscillations with respect to oscillations of .higher frequency appearing across said load circuit, manually operable means for continuously controlling the effectiveness of said attenuating means, and switching means operable by attenuation controlling movement of said manually operable means at at least one intermediate point of its range for controlling the effectiveness of said intensity increasing means.

, 2. In combination, aload circuit, means for supplying tosaid load circuit electric oscillations varying in frequency within. a band of audible frequencies in accordance with desired signals,

means for attenuating oscillations supplied to said load circuit at a first frequency within said band, separate means for increasing the intensity with respect to oscillations of other frequencies appearing across said load circuit of oscillations at a second frequency within said band, manually operable means for continuously controlling the; effectiveness of said attenuating means, and switching means operable by attenuation controlling movement of said manually operable means at at least one intermediate point of its range of movement for controlling the effectiveness of said intensity increasing means.

3. In combination, a load circuit, means for supplying to said load circuit electric oscillations varying in frequency within a band of audible frequencies in accordance with desired signals,

IS, an Moving to the right of its mid-posithe leftand decreased in moving to the right 01" th mid-position, rather than being decreased in both directions of movement as in Fig. 2. It will .be noted that at Figs. 2 and 3 the position or the potentiometer arm 20a at which attenuation of both high frequency and low frequency oscillations is a maximum occurs immediately to means for attenuating only oscillations of high frequency supplied to said circuit, separate means for attenuating oscillations of high and intermediate frequencies appearing acrosssaid cir-' cuit, manually operable means for continuously controlling the effectiveness of said first attenuating means, and switching means operable .by

attenuation controlling movement of said manu- -ally operable means at at least one intermediate point of its range of movement for controlling.

the effectiveness of said second attenuating means to decrease the intensity of low frequency oscillations appearing acrosssaid circuit.

4. In combination, a load circuit, means for 7' supplying to saidload circuit electric oscillations varying in frequency within. a band. of audible having at least two portions arranged to control frequencies in accordance, with desired signals,

means for attenuating high frequency oscillavarying in frequency within a band of audible frequencies in accordance with desired signals, meansfor attenuating high frequency oscillations supplied to said load circuit, separate means for increasing the intensity of low frequency oscillations with respect to oscillations of higher frequency appearing across said load circuit, manually operable means movable over a range the eifectiveness of said attenuating means within the same predetermined range of values and switching means controlled by movement of said manually-operable means to control the effectiveness of said intensity increasing means within each of said portions of its range of movement.

6. In combination, a load circuit, means for supplying to said load circuit electric oscillations varying in frequency within a band of audible frequencies in. accordance with desired signals, means for jattenuating oscillations supplied to said load circuit at afirst frequency within said band of frequencies, separate means for increasing the intensity with respect to oscillations of otherfrequencies appearing across said load circuit of oscillations ata second frequency within said band, manually operable means movable over a range having at least two similar portions arranged to control the effectiveness of said attenuating means within the same predetermined range of values, and switching means-controlled by movement of said manually operable means to control the 'eflectiveness of said intensity increasing means within each of said portions of the range of movement of said manually operable means.

7. In combination, a load circuit, means for supplying to said load circuit electric oscillations varying in frequency within a band of audible frequencies in accordance with desired signals, means for attenuating high frequency oscillations supplied to said circuit, separate means for increasing the intensity of low frequency oscillations with respect to oscillations of higher frequency appearing across said load circuit, manually operable means movable to either side of a predetermined intermediate position continuously to control the effectiveness of said attenuating means within a predetermined range, and switching mean's controlled by said manually operablemeans in accordance with its direction of movement from said intermediate position for selectably disabling or rendering operable said intensity increasing means.

8."In combination, a load circuit, means for supplying to said load circuit electric oscillations varying in frequency within a band of audible frequencies in accordance with desired signals, Y means. for attenuating high frequency oscillations impressed upon said circuit, separate means for increasing the-intensity of low frequency oscillations with respect to oscillations of higher frequency appearing across said circuit, a potentiometer impedance including a manually movable member and having two similar impedance sections on oppositesides of a predetermined intermediate position of said member, each of said impedance sections being connected continuously to control said attenuating means within the same predetermined control range, and switching means controlled by said manually movable member at said intermediate position for disabling said intensity increasing means whenever said manually movable member is on a selected one side of said intermediate position;

9. In a radio receiver, a volume control resistor, means for supplying to said resistor electric oscillations varying in frequency within a band of audible frequencies in accordance with desired signals, impedance means'including a capacitor connected across at least a portion of said resistor for decreasing the intensity of high and intermediate frequency oscillations appearing across said resistor, means including a potentiometer connected in parallel circuit relation with said resistor for controlling the intensity only of high frequency oscillations appearing across said resistor, said potentiometer including a manually operable member selectably cooperable with a pair of similar impedance sections arranged on opposite sides of a mid-'position of said manually operable member, said impedance sections being connected each continuously to control said high frequency oscillations within the same predetermined range, and

switching means actuated by said. manually operable member in passing from one of said sections to the other for short circuiting said capacitor whenever said manually operable member is on a selected side of said mid-position.

10. In combination, a load circuit, means for supplying to said load circuit electric oscillations varying in frequency within a band of .audible frequencies in accordance with desired signals,

means for attenuating high frequency oscillations supplied to said circuit, separate means for increasing the intensity of low frequency oscillations with respect to oscillations of higher frequency appearing across said load circuit, a

potentiometer'including a pair of similar impedance sections and a manually operable member movable within a predetermined range of movement for selective cooperation with said sections, said impedance sections being arranged on opposite sides of a predetermined intermediate position of said manually'operable member and being connected continuously to control the effectiveness of said attenuating means in opposite senses and within the samev predeter' mined range as said manually operable member is moved in opposite directions from said intermediate position, and switching means controlled by said manually operable member in accordance with its direction of movement from said intermediate position for selectably disabling or rendering operable said intensity increasing means.

11. In combination, a load circuit, means-for supplying to said load circuit electric oscillations varying in frequency within a band of audible frequencies in accordance with desired signals, means for attenuating high frequency oscillations supplied to said circuit, separate means for increasing the intensity of low frequency oscilla-' tions with respect to oscillations oi higher frequency appearing across said load circuit, a potentiometer including a pair of similar impedance sections and a manually operable member movable within a predetermined range of movement for selective'cooperation with said sections, said impedance sections being arranged on opposite sides of a predeterminedintermediate position of said manually operable member and being connected continuously to control; the effectiveness of said attenuating means in the same and within the same predetermined range as said manually operable member is moved in opposite directions from said intermediate position, and switching means controlled by said manually operable member in accordance with its direction of movement from. said intermediate position for selectably-disabling or rendering operable 'aaid intensity increasing means. a

CHARLES S. ROOT. 

